This invention concerns a device which allows a representative sample of a fluid stream to be withdrawn and desired characteristic properties analyzed. A particularly illustrative example, which we shall describe, is the application of this device to the evaluation of multi-phase fluid flow in a geothermal well stream.
Geothermal energy can be a promising alternative power source in selected parts of the world. In order to produce energy for commercial consumption, geothermal energy must be economically competitive with other conventional sources of energy. In order to attain this competitive position, the potential energy production from a candidate geothermal well must be accurately evaluated. Further, the determining characteristics of each well must be known in order to optimize equipment needs and power cycles to each well, thereby minimizing energy production costs. The geothermal well properties may be ascertained through measurement of specific chemical, physical, and thermal hydraulic parameters of the fluid flow such as phase composition, enthalpy, and mass flow rate. In carrying out these measurements, the device sampling means must withdraw a fluid specimen from the geothermal well stream such that the sample is representative of the entire fluid flow volume. Prior art has obtained fluid samples from geothermal wells via several probe configurations:
1. A single port probe fixed within pipe containing the geothermal well fluid stream (see F. A. Schraub, Two Phase Flow Instrumentation, Proc. of 11th National ASME/AICHE Heat Transfer Conference, August 1969, Minneapolis, Minn., pp. 47-57.)
2. A single port probe traversable across the fluid stream and retractable from the well pipe (see same reference as for no. 1).
3. A multiple port probe fixed with respect to the fluid stream and non-retractable from the stream (see R. T. Lahey, Jr., B. S. Shiralkar, and D. W. Radcliffe; Journal of Heat Transfer, 93, 197 (1971)).
The single port, non-retractable probe fixed within the well pipe would be suitable only for single phase flow or homogeneous multi-phase flow, neither of which exist in practice. Such a fixed probe could not examine the radial gradient of fluid flow in the pipe and would be subject to continuous exposure to the geothermal stream, resulting in substantial corrosion and erosion action.
The single port traversable probe with the retractable feature has two advantages over the fixed single port probe: the erosion and corrosion problem is greatly diminished as compared with permanent attachment inside the pipe, and the ability to traverse the probe does allow some measure of the radial gradient of fluid flow in the well pipe. However, there are inherent drawbacks to this system, including: (1) critical errors may be introduced by the speed and position control, (2) there is an inability to sample simultaneously an entire time-volume cross sectional element, (3) the moving probe results in changes in the back pressure on the sample line during the traverse which makes constant pressure sampling much more difficult, (4) at maximum extension the probe thickness must be rather large to prevent flutter or vibration and such size changes can cause misleading sampling results, and (5) since the quality and enthalpy of the mixture being withdrawn will vary during the traverse, the calorimeter analysis system will need to be designed to operate with transient inlet conditions.
Multiple-port fixed, non-etractable probes do allow sampling at a number of points in the fluid stream, thereby permitting mapping of the geothermal stream and allowing limited simultaneous sampling for the same time-volume element. Unfortunately, continuous exposure to the geothermal flow can result in enlargement or other unpredictable changes in port geometry and size. Finally, a sample representative of the entire fluid stream properties cannot be obtained by simply combining fluid samples from such a plurality of ports.
It is therefore an object of the invention to provide a fluid stream sampling device which has the ability to withdraw samples representative of the fluid stream.
It is a further object of the invention to provide a fluid stream sampling device with a plurality of sampling ports which are arranged to allow all fluid samples to be combined to produce a single sample representative of the entire fluid stream.
It is another object of the invention to provide a fluid stream sampling device which is capable of withdrawing a representative sample through a plurality of sampling ports of equal area, spaced variable distances apart, and having a constant ratio of port area to corresponding annular area sampled.
It is also an object of the invention to provide a fluid stream sampling device, which is capable of withdrawing a representative sample through a plurality of sampling ports of variable area, spaced equal distances apart, and having a constant ratio of port area to its corresponding annular area.
Additional objects, advantages and novel features of the invention will be set forth in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.